Method for treating a lens apt to trimming and lens apt to trimming

ABSTRACT

A method for treating an ophthalmic lens comprising two main sides, wherein at least one side comprises an organic or mineral external layer coated with a MgF 2  temporary protective layer, said method comprising the specific treating step of depositing the MgF 2  temporary protective layer on the external layer through vacuum evaporation at a speed lower than or equal to 0.5 nm/s. The lens obtained from the above method is capable of being submitted to a trimming operation within 48 hours after the ophthalmic lens has been treated, i.e. after the various layers have been deposited.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/341,167, filed Dec. 22, 2008, which is a continuation-in-part of U.S.application Ser. No. 10/524,206, filed Feb. 10, 2005, now U.S. Pat. No.7,488,509 which is a national phase application under 35 U.S.C. §371 ofPCT Application No. PCT/EP2003/007046 filed Jul. 2, 2003, which claimspriority to French Application No. 03/50216 filed Jun. 13, 2003. Thecontents of these applications are incorporated by reference

BACKGROUND OF THE INVENTION

The present invention relates to the field of trimming lenses, moreparticularly ophthalmic lenses.

An ophthalmic lens results from a succession of moulding and/orsurfacing/smoothing operations determining the geometry of both convexand concave optical surfaces of said lens, followed by appropriatesurface treatments

The last finishing step of an ophthalmic lens is the trimming operationconsisting in machining the edge or the periphery of the glass so as toshape it according to the required dimensions to adapt the lens to theglass frame wherein it is to be arranged.

Trimming is generally done on a grinding machine comprising diamondwheels that perform the machining step as defined hereinabove.

The lens is held, upon such an operation, by axially acting blockingmembers.

The relative motion of the lens with respect to the grinding wheel ismonitored, generally digitally, so as to provide the desired shape.

As it appears, it is mostly imperative that the lens be firmlymaintained upon such a movement.

To this end, before the trimming operation, an acorn-forming step isperformed on the lens, i.e. a holding means or acorn is positioned onthe convex surface of the lens.

A holding pad, such a self-adhesive chip, for example a two-sidedadhesive, is arranged between the acorn and the convex surface of thelens.

The so arranged lens is positioned on one of the above-mentioned axialblocking members, the second axial blocking member clamping then thelens on the concave surface thereof by means of an abutment, generallyconsisting in an elastomer.

Upon the machining step, a tangential torque effort is generated on thelens, which may result in a rotation of the lens relative to the acornif the lens holding means is not sufficiently efficient.

The good holding of the lens mainly depends on the good adhesion at theinterface of holding pad/convex surface of the lens.

The last generation ophthalmic lenses most often comprise an organic ormineral external layer modifying the surface energy, for exampleantistain hydrophobic and/or oilophobic coatings.

These are most often materials of the fluorosilane type reducing thesurface energy so as to avoid the adhesion of fatty stains, which arethus easier to be removed.

Such a surface coating type may be of such an efficiency that theadhesion at the pad/convex surface interface can be thereby altered,making difficult satisfactory trimming operations, in particular forpolycarbonate lenses the trimming of which generates much more largeefforts in comparison with other materials.

The consequence of a badly performed trimming operation is the pure andsimple loss of the lens.

That is why it is advantageous to deposit on the external layer atemporary protective layer imparting a surface energy at least equal to15 mJ/m², in particular a MgF₂ protective layer, such as disclosed inthe French Patent Application n^(o) 0106534.

Such a method is globally satisfactory, but can be further improved.Indeed, trimming lenses having their external layer coated with atemporary MgF₂ protective layer is often successfully possible only 48hours after the lens treatment i.e. after the various layers have beendeposited, in particular after the external layer and the protectivelayer have been deposited. When such lenses are trimmed in a period oftime of less than 48 hours, the acorn-holding pad system tends to detachitself from the lens spontaneously or under a very weak effort. This isthe “acorn-removing” phenomenon. Practically, this occurs when the lensis removed from the grinding machine.

SUMMARY OF THE INVENTION

One of the objects of the invention has therefore the aim to provide amethod for treating a lens comprising an organic or mineral externallayer, in particular an hydrophobic and/or oilophobic layer, coated witha MgF₂ temporary protective layer, enabling to perform the trimmingoperation very quickly after the various layers have been deposited onthe lens, for example, after one hour.

To this end, the invention relates to a method for treating anophthalmic lens comprising two main sides, wherein at least one sidecomprises an organic or mineral external layer coated with a MgF₂temporary protective layer, the method comprising a specific treatmentstep selected amongst the following steps:

-   -   a liquid phase chemical treatment of the temporary protective        layer, leading to the formation of MgO and/or Mg(OH)₂ in and/or        on the temporary protective layer,    -   a deposit of at least one non fluorinated metallic oxide and/or        of at least one non fluorinated metallic hydroxide on the        temporary protective layer through transfer thereof from an        electrostatic film or through vacuum evaporation thereof        directly on the temporary protective layer,    -   the deposit of the MgF₂ temporary protective layer on the        external layer is performed through vacuum evaporation at a        speed lower than 0.5 nm/s, preferably lower than or equal to 0.3        nm/s.

Preferably, the metallic oxide is selected amongst calcium or magnesiumoxide, praseodymium oxide, cerium oxide or a mixture of two or more ofsuch oxides.

Preferably, the metallic hydroxide is the magnesium hydroxide.

The external layer is preferably a hydrophobic and/or oilophobic surfacecoating and, in particular, a hydrophobic and/or oilophobic surfacecoating deposited on a mono- or multilayered non reflecting coating.

As previously indicated, the hydrophobic and/or oilophobic coatings areobtained through application, on the non reflecting coating surface, ofcompounds reducing the lens surface energy.

Such compounds have been widely disclosed in the previous art, forexample in U.S. Pat. No. 4,410,563, EP-0203730, EP-749021, EP-844265,EP-933377.

Silane-based compounds bearing fluorinated groups, in particularperfluorocarbone or perfluoropolyether group(s), are most often used.

By way of examples, silazane, polysilazane or silicone compounds are tobe mentioned, comprising one or more fluorinated groups such as thosementioned hereabove.

A known method consists in depositing on the non reflecting coatingcompounds bearing fluorinated groups and Si—R groups, R representing an—OH group or a precursor thereof, preferably an alkoxy group. Suchcompounds may perform, at the non reflecting coating surface, directlyor after hydrolysis, polymerization and/or cross-linking reactions.

Applying compounds reducing the lens surface energy conventionallyoccurs by dipping in a solution of said compound, centrifugation orvapour phase depositing, amongst others. Generally, the hydrophobicand/or oilophobic coating has a thickness lower than 30 nm, preferablyranging from 1 to 20 nm, more preferably ranging from 1 to 10 nm.

The invention is preferably carried out with lenses comprising ahydrophobic and/or oilophobic surface coating imparting a surface energylower than 14 mJoules/m² and more preferably lower than or equal to 12mJ/m² (the surface energies being calculated according to theOwens-Wendt method disclosed in the following reference: “Estimation ofthe surface force energy of polymers” Owens D. K., Wendt R. G. (1969),J. APPL. POLYM. SCI, 13, 1741-1747).

The MgF₂ temporary protective layer is deposited directly on theexternal layer.

The protective layer may be deposited using any appropriate conventionalmethod, in vapour phase (vacuum deposit), or in liquid phase, forexample, through vaporization, centrifugation or dipping.

Generally, non reflecting hydrophobic and/or oilophobic coatings havebeen deposited by evaporation in vacuum caps and it is desirable todeposit the temporary protective layer with the same method, making itpossible to perform all the operations successively, with no excessivehandling of the lenses between the steps.

Another advantage of the vacuum deposit is to avoid any wettabilityproblem in the case where the thin layer onto which the protective layerhas just been deposited shows hydrophobic and/or oilophobic properties.

Generally speaking, the temporary protective layer should have asatisfactory thickness so as to avoid any subsequent alteration of theexternal layer properties during the various treating steps of the lens.

Preferably, its thickness ranges from 5 to 50 nm.

The MgF₂ temporary protective layer will increase the lens surfaceenergy up to a value of at least 15 mJoules/m².

It can be applied on an area covering the whole of at least one of thetwo sides of the lens or only on the area adapted to accommodate thecontact of the holding pad of said lens.

More precisely, it is usual to deposit the holding pad, associated withthe acorn, on the lens convex side. It is therefore possible to coverwith the protective layer the whole convex side or, alternatively, onlya central area of the convex side, using a mask or any other appropriatetechnique.

Moreover, the lenses having a MgF₂ temporary protective layer may besubjected to markings using various inks, commonly used by the man ofthe art for progressive lenses.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings form part of the present specification and areincluded to further demonstrate certain aspects of the presentinvention. The invention may be better understood by reference to one ormore of these drawings in combination with the detailed description ofspecific embodiments presented below.

FIG. 1. Curve 1 illustrates a lens which has not been subjected to aspecific treatment step. Curve 2 illustrates a lens which has beensubjected to a specific treatment step by a sodium hypochlorite aqueoussolution.

FIG. 2. The abscissa represents the time T elapsed since the end of thelens treatment (expressed in hours), and the ordinate represents theholding time of the pad under the water jet (expressed in seconds).

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

As previously described, the method according to the invention comprisesa specific treating step.

When the specific treating step according to the invention is a liquidphase chemical treatment of the temporary protective layer, such aliquid phase chemical treatment can be performed using severalembodiments.

According to a first preferred embodiment, the liquid phase chemicaltreatment comprises a step of contacting the MgF₂ temporary protectivelayer with non distilled non deionized water (for example tap water) ata temperature from 30 to 50° C., preferably from 30 to 40° C.

According to a second preferred embodiment, the liquid phase chemicaltreatment comprises a step of contacting the MgF₂ temporary protectivelayer with a soda aqueous solution.

During the contact step, the aqueous solution temperature advantageouslyranges from 14 to 40° C., and more preferably from 14 to 20° C.

Preferably, the soda molar concentration of the solution ranges from0.01 to 0.1 mol/liter and preferably in the order of 0.02 mol/liter.

According to a third preferred embodiment, the liquid phase chemicaltreatment comprises a step of contacting the MgF₂ temporary protectivelayer with a sodium hypochlorite aqueous solution.

As previously, the aqueous solution temperature advantageously rangesfrom 14 to 40° C., and preferably from 14 to 20° C.

Preferably, the sodium hypochlorite solution has a chlorometric degreefrom 0.1 to 5, preferably in the order of 1.

Generally, in the three previously described embodiments, the step ofcontacting the MgF₂ temporary protective layer with non distilled nondeionized water, or with the soda aqueous solution or the sodiumhypochlorite occurs during a period of time at least equal to 10seconds, preferably in the order of 15 seconds.

Moreover, preferably, the liquid phase chemical treatment subsequentlycomprises a water rinsing step, preferably using deionized or distilledwater, and a drying step, for example, through air blowing.

As previously stated, the specific treating step according to theinvention may also consist in depositing at least one non fluorinatedmetallic oxide and/or at least one non fluorinated metallic hydroxide onthe temporary protective layer. Preferably, a MgO deposit is carriedout. The depositing technique will be described in the case of MgO.Nevertheless, the mentioned techniques and thicknesses also apply toother non fluorinated metallic oxides and metallic hydroxides on thetemporary protective layer. MgO depositing may be performed according totwo preferred embodiments.

According to a first preferred embodiment, MgO depositing is made bytransfer and comprises the following steps of:

-   -   vacuum evaporating MgO on an electrostatic film,    -   depositing the electrostatic film onto the lens side coated with        the MgF₂ temporary protective layer,    -   removing the electrostatic film, MgO remaining on MgF₂.

The electrostatic film removal is generally performed just beforetrimming. Thus, between the film depositing and its removal, the film,in addition to the fact that it allows the MgO to be transferred ontothe temporary protective layer, also makes it possible to ensure theprotection of the temporary protective layer when the lens is beingstored or transported.

According to a second preferred embodiment, MgO depositing onto thetemporary protective layer occurs through vacuum evaporation, the shapedMgO layer having a thickness ranging from 1 to 5 nm.

The evaporated MgO can result, for example, from an evaporation from:

-   -   MgO granules, with a granulometry ranging from 1 to 3 mm (ref.:        M-1131 from CERAC);    -   MgO granules, with a granulometry ranging from 3 to 6 mm (ref.:        M-2013 from UMICORE);    -   MgO pellets, (ref.: 0481263 commercialized by UMICORE        corporation).

When Mg(OH)₂) is evaporated, it can be advantageously obtained fromALDRICH.

Generally, MgO depositing occurs after the MgF₂ deposit. Thus, twodistinct MgF₂/MgO layers are achieved. This can be, if necessary,followed with part of the MgF₂ evaporation, starting with the MgOevaporation, so that there is then a gradient the composition of whichvaries from pure MgF₂ to pure MgO at the surface.

Finally, as previously stated, the specific treating step can alsoconsist in slowing down the MgF₂ temporary protective layer on theexternal layer. Usually, such a type of deposit is performed at a speedof about 0.5 nm/s. According to the invention, depositing the protectivelayer through vacuum evaporation is performed at a speed lower than 0.5nm/s, preferably about 0.1 nm/s.

As previously indicated, the lenses treated with the method according tothe invention comprise two main sides, one of which comprises anexternal layer coated with a temporary MgF₂ protective layer.

According to a preferred embodiment, the two main sides comprise anexternal layer coated with a MgF₂ temporary protective layer. Generally,the first side on which the various layers are deposited is the concaveside. The MgF₂ layer then makes it possible to protect such a side whilethe second side is being treated.

When both main sides comprise an external layer covered with a MgF₂protective layer, the specific treating step according to the inventionis preferably carried out on each of the main sides.

After the various treating operations of the lens, in particular afterthe lens has been trimmed, the temporary protective layer is removed.

The removal step of the temporary protective layer can be carried outeither in a liquid medium, or through a mechanical action, such asfriction, dry wiping, or through by implementation of those two means.

At the end of the step of removing the temporary protective layer, thelens exhibits optical and surface features of the same order, evennearly identical to those of the initial lens, comprising thehydrophobic and/or oilophobic coating.

The present invention also relates to an ophthalmic lens comprising ahydrophobic and/or oilophobic coating, a MgF₂ temporary protectivelayer, deposited on said hydrophobic and/or oilophobic coating,characterized in that a layer of at least one non fluorinated metallicoxide and/or at least one non fluorinated metallic hydroxide isdeposited on the MgF₂ protective layer.

The non fluorinated metallic oxides and hydroxides are preferablyselected amongst those previously described, and more particularly, thenon fluorinated metallic hydroxide is magnesium hydroxide.

The hydrophobic and/or oilophobic coating is such as previously definedand the external layer is preferably deposited on a non reflectingcoating, in particular multilayered.

The invention also relates to an ophthalmic lens such as hereinabovedefined comprising an easily detachable electrostatic film covering thenon fluorinated metallic oxide and/or hydroxide layer as previouslydescribed.

Preferably, the layer coated with the electrostatic film is a MgO layer.

The present invention is illustrated by the following examples,referring in particular to FIGS. 1 and 2, representing the holding timeof a pad glued to a lens under water jet, as a function of the timeelapsed from the deposit of the external layer and the protective layer.

EXAMPLES Example 1

The aim is to test the specific treating effect according to theinvention upon the lens trimming operation, in particular on theacorn-removing phenomenon.

The deposits are achieved on substrates which are CR39® based ophthalmiclenses comprising, on both sides, an anti-abrasion coating of thepolysiloxane type corresponding to example 3 in the Patent ApplicationEP 614957. The lenses are washed in an ultra-sound cleaning vessel,steamed for 3 hours minimum at a temperature at 100° C. They are thenready to be treated. The treated lenses are round lenses.

1. Preparation of the Lenses

1.1 Preparation of the Lenses Having a Non Reflecting andHydrophobic/Oilophobic Coating

The vacuum treating machine used is a Balzers BAK760 machine providedwith an electron gun, an ion gun of the “end-Hall” Mark2 Commonwealthtype and an evaporation source with a Joule effect.

The lenses are placed on a carrousel provided with circular openingsintended to accommodate the lenses to be treated, the concave sidefacing the evaporation sources and the ion gun.

A vacuum drawing is performed until a secondary vacuum is reached.

Then, a successive evaporation is performed, with the electron gun, of 4non reflecting optical layers, high index (IH), low index (BI), HI, BI:ZrO₂, SiO₂, ZrO₂, SiO₂.

Finally, a hydrophobic and oilophobic coating layer is deposited throughevaporation of a product with the tradename OPTOOL DSX (compoundcomprising perfluoropropylene patterns) sold by DAIKIN corporation.

A given amount of Optool DSX is placed in a copper capsule with a 18 mmdiameter, in turn placed in a joule effect crucible (tantalum crucible).

A 1 to 5 nm thickness of hydrophobic and oilophobic coating is depositedthrough evaporation.

Setting the deposited thickness is performed by means of a quartz scale.

1.2 Deposit of the Temporary Protective Layer

The protective layer is then evaporated.

The deposited material is a compound with MgF₂ formula, having a 1 to2.5 nm granulometry, sold by Merck corporation.

The evaporation is performed using an electron gun.

The deposited physical thickness is 20 nm, with a deposit speed equal to0.52 nm/s.

Setting the deposited thickness is performed by means of a quartz scale.

Subsequently, the enclosure is heated again and the treatment chamber isset back to atmosphere.

The lenses are then turned upside down and the convex side orientedtowards the treatment area. The convex side is treated identically tothe concave side (reproducing the steps 1.1 and 1.2 hereabove).

1.3 Specific Treatment Step

The lenses are then subjected to a specific treatment step according tothe invention selected amongst the following steps:

-   -   non deionized and non distilled water    -   sodium hypochlorite aqueous solution    -   soda aqueous solution    -   MgO transfer from an electrostatic film    -   MgO evaporation directly on the temporary MgF₂ layer.

a) (non deionized and non distilled) warm water

The lenses are placed under the tap warm water, with a 40° C.temperature, for 15 seconds.

Then, they are rinsed with distilled water and blown with pressurizedair.

b) Sodium hypochlorite aqueous solution

The lenses are dipped for 15 seconds in a Pyrex® vessel containing 1liter distilled water with a temperature equal to 40° C. and 20 ml ofJavel extract at 48 chlorometric degrees.

Then, the lenses are rinsed with distilled water and blown withpressurized air.

c) Soda aqueous solution

The lenses are immerged for 15 seconds in a Pyrex® vessel containing 1liter distilled water with a temperature equal to 40° C. and 40 ml ofsoda at 0.5 mol·L⁻¹.

Then, the lenses are rinsed with distilled water and blown withpressurized air.

d) MgO transfer from an electrostatic film

With an electron gun, a MgO layer is vacuum evaporated from MgO chips(reference 0481263) from the UMICORE corporation on PVC based(polyvinylchloride) copolymer electrostatic films with a 100/μmthickness, supplied from SERICOM PLASTOREX corporation. Such films arepresent in the form of discs with a diameter ranging from 38 to 50 mm.

The MgO coated electrostatic films are deposited on the lens convexside.

At the trimming time, the films are removed. A MgO layer remains on theMgF₂ protective layer.

e) MgO evaporation directly on the MgF₂ temporary layer.

Using an electron gun, a MgO layer is vacuum evaporated (from MgO chips(reference 0481263) from UMICORE corporation) with a 2 nm thickness,directly on the MgF₂ protective layer.

2. A Corn-Removing Test

2.1 Principle

An acorn-removing test is performed under a water jet on the preparedlenses. This test is simpler and quicker to perform than trimming thelenses. It is also “harder” than the real trimming of the lenses.Nevertheless, it makes it possible to classify the results in a verydiscriminating way.

A double-sided 3M brand self-adhesive chip is used as a holding pad.

The pad is manually glued on the acorn.

The acorn+pad set is manually glued on the convex side of each lens.

The lens is placed under tap water (running water), the temperature ofwhich is not monitored, for more than 5 minutes. The flow rate is 6liter/minute. The distance between the lens and the tap nose isapproximately 20 cm.

Alternatively, a hand rotation of the lens is performed, as well as atilting operation, so that the water penetrates through the edge andalso through the central hole of the acorn.

If the acorn+pad set falls before 5 minutes (corresponding to theacorn-removing phenomenon), the time is recorded during which the sethas remained glued on the lens.

If after 5 minutes, the acorn+pad set has not fallen, the percentage isrecorded of the pad surface remaining still glued. This is well visiblethrough transmission looking at the lens from the concave side underneon light.

2.2 Tests and results

a) Test 1

The holding time of the acorn+pad set is measured under the water jet,as a function of the elapsed time from the end of the lens treatment,i.e. as from the deposit of the various layers and the specifictreatment step.

The results are represented on FIG. 1.

The measurements are made for a lens which has not been subjected to thespecific treatment step (curve 1), and for a lens having been subjectedto the specific treatment step by the sodium hypochlorite aqueoussolution (curve 2).

The abscissa represents the time elapsed since the end of the lenstreatment. The ordinate represents the pad holding time under the waterjet in seconds.

It can be seen that after one hour, the lens having been subjected tothe specific treatment step reaches a pad holding time of 300 seconds,whereas it takes 2 weeks for the glass which has not been subjected tothe specific treatment step to achieve the same holding time.

b) Test 2

The holding time measurements are performed for lenses which have notbeen subjected to a specific treatment step according to the inventionand for lenses having been subjected to a specific treatment stepaccording to the invention. The measurements are made at various times Tafter the end of the treatment of the lens.

The results are gathered in table 1.

TABLE 1 ACORN-REMOVING UNDER A WATER JET Specific treatment 1 h < T < 2step T = 1 hour weeks T > 2 weeks None Acorn-removing Acorn-removing Noacorn- after 10 s for 1 m after 10 s for 5 m removing after under thewater under the water 5 m under the jet jet water jet Warm tap water, NoNo No or soda aqueous solution or sodium hypochlorite aqueous solutionMgO transfer No No No MgO evaporation No No No

The results on table 1 show that the specific treatment step accordingto the invention completely eliminates the acorn-removing phenomenon.

c) Test 3

In this test, the specific treatment step by the sodium hypochloriteaqueous solution such as previously described has been performed on onlyhalf of the lens surface.

Thus, the lenses have been half immerged in a Pyrex flask containing thesodium hypochlorite aqueous solution.

After approximately 15 seconds under the water jet, the pads glued onhalf of the lens surface which have not been subjected to the specifictreatment step are completely peeled off.

After 5 minutes under the water jet, the pads glued on half of the lenssurface having been subjected to the specific treatment step remainglued at 100%.

The same result is obtained in the case where the specific treatmentstep is performed with the soda aqueous solution.

Examples 2A (Comparative), 2B and 2C Comparative Example 2A

Lenses comprising an antireflection coating and a hydrophobic/oilophobiccoating (“top coat”) were prepared as described in §1.1 of example 1.The physical thickness of the deposited top coat was 2 nm. A 20 nm thickMgF₂ temporary protective layer was then deposited onto said top coat asdescribed in §1.2 of example 1, except that the deposition speed was0.53 nm/s instead of 0.52 nm/s.

Example 2B

Lenses were prepared as described in comparative example 2A, except thatthe deposition speed of the MgF₂ temporary protective layer was 0.10nm/s instead of 0.53 nm/s. This step is a specific treating stepaccording to the invention (deposition through vacuum evaporation at aspeed lower than 0.5 nm/s).

Example 2C

Lenses were prepared as described in example 2B, except that thedeposition speed of the MgF₂ temporary protective layer was 0.03 nm/sinstead of 0.10 nm/s. This step is a specific treating step according tothe invention (deposition through vacuum evaporation at a speed lowerthan 0.5 nm/s).

Test and Results

The lenses of comparative example 2A and examples 2B and 2C weresubjected to the acorn-removing test disclosed in §2.1 of example 1, atvarious times T after the end of the lens treatment.

The results are presented on FIG. 2 (the abscissa represents the time Telapsed since the end of the lens treatment (expressed in hours), andthe ordinate represents the holding time of the pad under the water jet(expressed in second).

As can be seen, the lenses of example 2B (having been subjected to aspecific treatment step according to the invention) reach after roughlyT=1 hour a pad holding time of 300 seconds, whereas it takesapproximately two weeks (168 h) for lenses according to comparativeexample 2A to achieve the same holding time. The same results wereobtained for examples 2B and 2C (data not shown on FIG. 2).

1. A method for treating an ophthalmic lens comprising two main sidesand having at least one side comprising an organic or mineral externallayer coated with a MgF₂ temporary protective layer, wherein treatingcomprises depositing the MgF₂ temporary protective layer on the externallayer through vacuum evaporation at a speed lower than 0.5 nm/s.
 2. Themethod of claim 1, wherein the speed is lower than or equal to 0.3 nm/s.3. The method of claim 1, wherein the external layer is a hydrophobicand/or oilophobic surface coating.
 4. The method of claim 1, wherein theexternal layer has a thickness lower than 30 nm.
 5. The method of claim4, wherein the external layer has a thickness ranging from 1 to 20 nm.6. The method of claim 5, wherein the external layer has a thicknessranging from 1 to 10 nm.
 7. The method of claim 1, wherein the externallayer is on a non-reflecting coating.
 8. The method of claim 7, whereinthe non-reflecting coating is multi-layered.
 9. The method of claim 1,wherein the temporary protective layer has a thickness ranging from 5 to50 nm.
 10. The method of claim 1, wherein both main sides of theophthalmic lens comprise an external layer coated with a MgF₂ temporaryprotective layer.
 11. The method of claim 1, further comprising trimmingthe ophthalmic lens after it has been treated.
 12. The method of claim11, wherein the trimming is performed within 48 hours after theophthalmic lens has been treated.